Problem: Solve for $r$ : $23 = 25 + r$
Explanation: Subtract $25$ from both sides: $ \begin{eqnarray} \\ \hphantom{23 {- 25}} &\hphantom{=}& \hphantom{r} \\ 23 &=& 25 + r \\ \\ {-25} && {-25} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ 23 {- 25} &=& r \\ \end{eqnarray} $ Simplify. $ r = -2$